Trunk muscle co-ordination during gait: Relationship between muscle function and acute low back pain

Low back pain costs billions of Euros annually in all industrialized countries. Often radiological diagnosis fails to give evidence of the pathogenesis of low back pain. Although psychophysiological characteristics have an influence, it seems that insufficient muscular spinal stabilization may play the major role in the development of low back pain. Assessment of trunk muscle stabilization activity during everyday activities is rare. Therefore, in this study healthy persons were investigated during walking on a treadmill at a speed of 4 km/h. Women (n = 16) with no history of back pain were investigated before and after a static loading situation of the spine, i.e. while wearing a waistcoat. After this loading situation four women developed pain (pain subjects). Surface EMG (SEMG) was taken from five trunk muscles of both sides. Grand averaged amplitude curves over stride, amplitude normalized curves and variation between all included strides were calculated for all muscles and subjects, respectively. The normal range of all calculated parameters was defined within the span between the 5th and the 95th percentiles of all pain free subjects. Data were evaluated according to deviations from the normal range.

Already before the load situation, pain subjects showed considerable deviations from the normal range, mainly of their abdominal muscles. There was no relationship between magnitude of deviation and pain intensity, but perceived exertion was highest in those subjects who showed the most symptoms in terms of number of muscles being identified as considerably deviating from the normal range. No specific “dysfunction pattern” could be identified, which argues for highly individual mechanisms instead of a single target muscle. The results suggest cumulative effects of different disturbance levels resulting in acute back pain. Since deviations could be identified already before the pain occurred, disturbed muscle function seems to be a risk factor for developing back pain. Further investigations aimed at clear identification of and, as a second step, correction of muscle function are necessary.     

Relationship between erector spinae static endurance and muscle oxygenation-blood volume changes in healthy and low back pain subjects

The purposes of this study were to: (1) compare the muscle blood volume (Mbv) and oxygenation (Mox) responses on the right and left side erector spinae during the Biering-Sorensen muscle endurance (BSME) test between healthy, low back pain active (LBP-A) and LBP-sedentary (LBP-S) subjects using near infrared spectroscopy (NIRS), and (2) determine the relationships between the BSME time and Mbv and Mox. Informed consent was obtained from 30 healthy and 30 chronic LBP subjects. The latter group was subdivided into an active (LBP-A; n = 18) and sedentary (LBP-S; n = 12) subgroups based on physical activity patterns. The groups were age and sex matched. The NIRS probes were placed bilaterally on the erector spinae muscle at the level of the third lumbar vertebrae. The testing protocol was: 2-min resting baseline, BSME to voluntary fatigue, and 4-min recovery. During the BSME Mbv immediately increased for approximately 30-60 s, then showed an asymptote, and a steady decline towards the baseline at termination. Mox demonstrated either an initial increase followed by a systematic decrease until the termination of the BSME, or a systematic decrease throughout the BSME until termination. The LBP-S subjects showed a reduced Mox-range and slower Mox (1/2) recovery time on the left side suggesting a reduced aerobic capacity of the erector spinae muscle in this group. Significant correlations were noted between BSME time and the pooled values of Mox-delta and-range only in the LBP-A group. These observations suggest that factors other than erector spinae aerobic capacity can influence BSME performance.     

Individual factors and physical work load in relation to sensory thresholds in a middle-aged general population sample

The aim of this study was to explore individual and occupational factors possibly related to sensory thresholds in 484 middle-aged men and women from the general population. Multivariate analyses were performed using a linear model including eight covariates (age, body height, skin temperature, smoking habits, musculoskeletal symptoms during the last week before examination, isometric muscle strength, aerobic capacity, and average physical work load during the last 15 years). Men and women were considered separately in all analyses. Major findings were as follows: pressure pain thresholds increased with muscle strength; cold perception thresholds on the foot improved with increasing skin temperature; vibration and warm perception thresholds on the foot increased with age and body height; pressure pain threshold on the leg was decreased and vibration threshold on the hand was increased in women with musculoskeletal symptoms; pressure pain thresholds were slightly increased in men reporting long-lasting high physical work load. Significant sex differences were found for the majority of sensory thresholds, that is higher thresholds in men. However, body height was found to be more important than gender for differences in vibration and warm perception thresholds on the foot. Electronic Publication     

Spectral analysis of electromyogram in lumbar muscles: fatigue induced endurance contraction

In the last few years, epidemiological studies have shown correlations between the low endurance capacity of the erector spinae muscle and low back pain (LBP). In this study, the function of the erector spinae muscle and localized muscle fatigue in LBP were investigated in both LBP patients and control subjects without LBP, using surface multi-channel electromyograms (EMG). Four positions (L1, L2, L4, L5) were chosen as representative locations for the different functions of the erector spinae muscle. Median frequency (f _m) parameters of an EMG power density spectrum were monitored to quantify localized muscle fatigue. This research indicated a statistically significant difference (P < 0.05) in f _m, parameters between the LBP patients and the control subjects. The integrated electromyogram (iEMG) signals of LBP patients were considerably higher than for the control subjects during endurance isometric contraction. Our research suggested that human fatiguing erector spinae muscle, in submaximal voluntary contractions tests, induced a different firing order of motor unit spikes between two groups.     

Musculoskeletal capacity of middle-aged women and men in physical,mental and mixed occupations

Summary The musculoskeletal capacity of 44 women and 39 men, mean age 55.0±3.4 years, was studied at the beginning and end of a 3.5 year period. The measurements included anthropometrics, maximal isometric trunk flexion and extension strength, maximal isometric hand grip strength and back mobility. According to a job analysis the subjects were divided into three dominating work groups: physical, mental and mixed groups. The results showed significant changes in anthropometrics, maximal isometric muscle strength and in mobility. The body weight and body mass index among women and the body mass index among men increased significantly during the period. The body height and sum of the skinfolds had on the other hand decreased significantly for both women and men. Women showed significant decreases of 9% and 10% (p<0.05 andp<0.01) in isometric trunk flexion and extension strength, and an increase of 9% in back mobility (p<0.05). In mental work, most of the significant changes occurred among women. Men had significant decreases in isometric trunk flexion and extension, 22% and 16% respectively (p<0.001) and an increase of 13% in back mobility (p<0.001). The men doing physical work had most of the significant changes in musculoskeletal capacity. The results revealed accelerated changes in musculoskeletal capacity in middle-aged employees.     

Effect of one-legged exercise on the strength,power and endurance of the contralateral leg

Summary The purpose of this investigation was to study the effect of one-legged exercise on the strength, power and endurance of the contralateral leg. The performance of the knee extensor and flexor muscle of 20 healthy young adults (10 men and 10 women) was first tested by Cybex II+ and 340 dynamometers. Then 10 subjects were chosen at random to train using one leg three times a week for 7 weeks whilst the other 10 served as controls. During the 8th week, the tests were repeated. Both quadriceps and hamstring muscles of the trained subjects showed a cross-transfer effect from the trained limb to the untrained side. This concerned the strength and power, as well as endurance characteristics of these muscles. The average change in peak torque of the quadriceps muscle was + 19% (P<0.001) in the trained limb, + 11% (P<0.01) in the untrained limb and 0% in the control limbs. In hamstring muscles the changes were + 14% (P<0.01), + 5% and –1%, respectively. Concerning muscle endurance (work performed during the last 5 contractions in the 25-repetition test) the corresponding changes were + 15% (P<0.01), +7% (P<0.01), and –1% in quadriceps muscle, and + 17% (P<0.05), +7%, and –3% in hamstring muscles. The average strength benefit in the untrained limb was +36% (hamstring muscles) and +58% (quadriceps muscle) of that achieved in the trained limb. Untrained hamstring muscle showed better benefits in the endurance parameters than in strength or power parameters, while in the quadriceps muscle this effect was reversed. A positive relationship was observed between the changes (greater improvement in the trained limb resulted in greater improvement in the untrained limb) (hamstring muscles:r=0.83,P<0.001, quadriceps muscle:r=0.53,P<0.001). In endurance parameters, this relationship was almost linear while in the strength and power parameters the results were more in favour of a curvilinear relationship with limited benefit.     

Differences in quadriceps muscle strength and fatigue between lean and obese subjects

The present study aimed to compare quadriceps femoris muscle strength and fatigue between obese (grade II and III) and nonobese adults. Ten obese (mean age: 25 years; mean BMI: 41 kg/m2) and ten lean (mean age: 27 years; mean BMI: 23 kg/m2) men were tested. Quadriceps muscle fatigue was quantified as the (percent) torque loss during a voluntary isokinetic (50 maximal contractions at 180°/s) and an electrostimulated (40 Hz) isometric protocol (5 min, 10% of the maximal torque). Maximal voluntary isometric and isokinetic torque and power were also measured. Voluntary torque loss was significantly higher (P < 0.05) in obese (−63.5%) than in lean subjects (−50.6%). Stimulated torque decreased significantly (P < 0.05) but equally in the two subject groups. Obese subjects displayed higher absolute (+20%; P < 0.01) but lower relative (i.e., normalized to body mass) (−32%; P < 0.001) muscle torque and power than their lean counterparts. Obese individuals demonstrated lower fatigue resistance during voluntary but not during stimulated knee extensions compared to their nonobese counterparts. Peripheral mechanisms of muscle fatigue—at least those associated to the present stimulated test—were not influenced by obesity. The observed quadriceps muscle function impairments (voluntary fatigue and relative strength) probably contribute to the reduced functional capacity of obese subjects during daily living activities.     

Prediction of physical activity level in adulthood by physical characteristics,physical performance and physical activity in adolescence: an 11-year follow-up study

The purpose of the study was to investigate to what extent the physical activity pattern in adulthood can be predicted by physical characteristics, performance and activity in adolescence. A group of 62 men and 43 women completed a questionnaire concerning physical activity during their leisure time at the ages of 16 and 27 years. An activity index produced from the questionnaire. At the age of 16 years, the subjects were also tested for strength (strength test battery) and running performance (9-min run). Maximal oxygen uptake ( ) was estimated from a submaximal test and a muscle biopsy specimen was taken and analysed for fibre types (percentages of types I, IIA, 1113). The proportion of subjects engaged in some kind of physical activity during their leisure time was approximately 70% among the women and 80% among the men at both ages. The time spent on physical activity (minutes per week) decreased with age for the men but not for the women. The women devoted less time. to physical activity than the men both at age 16 and 27 years. The attitude to endurance activities had changed to a more positive attitude among the women and to a less positive attitude among the men at age 27 years. The aerobic potential ( and percentage of type I fibre), running performance, strength performance, physical activity and marks in physical education at age 16 years explained 82% of the physical activity level in adulthood for the women and 47% for the men. The aerobic potential at age 16 years alone explained 31% of the adult physical activity level in the women and 24% in the men. Strength performance, physical activity and marks in physical education at age 16 years further increased the predictive value for the physical activity level in adulthood for the women but not for the men. It is suggested that the major portion of the variation in physical activity level in adult women, but not in the adult men, could be predicted from physical characteristics, physical performance, and the activity level in adolescence.     

Back and neck extensor loading and back pain provocation in urban bus drivers with and without low back pain

This study assessed low back and trapezius muscle activity in bus drivers, with or without recurrent low back pain (LBP), during the long term driving. In addition, low back and neck–shoulder pain intensities and fatigue were measured and the effect of low back support was observed. Also the possible source of LBP was attempted to assess by vibration pain provocation test and lumbar MRI.

Forty bus drivers (recurrent LBP n = 25) participated in this study. Low back and neck–shoulder pain and subjective fatigue intensity was assessed by visual analogue scales (VAS) before and after driving. Lumbar paraspinal and trapezius muscle activation during driving was measured by surface EMG. Vibration pain provocation test was applied for all subjects.

Average paraspinal myoelectric activity during driving was approximately 1% of MVC in both groups. Average trapezius myoelectric activity during driving was from 2 to 4% of MVC. Trapezius muscle activity was higher in back healthy drivers than in those with LBP. The low back support had no effect either on paraspinal or trapezius EMG activity. Low back and neck–shoulder fatigue increased during driving in both groups especially in those subjects with positive vibration pain provocation. The neck–shoulder pain and fatigue were more severe in drivers suffering from LBP. Low back support had no effect on low back and neck–shoulder subjective fatigue and neck–shoulder pain but tended to limit the LBP increase during driving. Paraspinal muscle loading in urban bus drivers was very limited and either LBP or ergonomic low back support had no effect on it. Trapezius muscle seemed to be less active in drivers suffering from recurrent LBP. Internal disc disruptions may expose to pain and fatigability during driving.     

Low back muscle fatigue during Sørensen endurance test in patients with chronic low back pain: relationship between electromyographic spectral compression and anthropometric characteristics

This study assessed low back muscle fatigue during S?rensen back endurance test in chronic low back pain (CLBP) patients and healthy controls, and investigated relationship between the erector spinae muscle fatigability and subject's anthropometric characteristics. Four groups (n = 10 per group) of middle-aged (47-52-year-old) subjects participated: 1) female CLBP patients, 2) healthy female subjects, 3) male CLBP patients and 4) healthy male subjects. Subjects performed S?rensen back endurance test until exhaustion, while electromyographic (EMG) power spectrum median frequency compression over time (MF slope) as indicator of the erector spinae muscle fatigability, and endurance time were recorded. The endurance time was shorter (p < 0.05) in male CLBP patients compared to the healthy male and female subjects. No significant gender differences in endurance time were found in CLBP patients and in healthy subjects. EMG power spectrum MF slope did not differ significantly in CLBP patients and in healthy subjects. However, MF slope was higher (p < 0.05) in healthy male than in female subjects. Body mass and BMI correlated moderately positively with MF slope (r = 0.40-0.67) in all measured groups. We conclude that male CLBP patients had lower back extensor muscle isometric endurance compared to the healthy subjects of both genders, whereas no gender differences in isometric endurance were found in CLBP patients and in healthy subjects. Healthy male subjects had greater lumbar erector spinae muscle fatigability compared to the healthy female subjects. Subjects with higher body mass and body mass index fatigued faster during S?rensen back endurance test.     

Hemodynamic and hormonal responses to lower body negative pressure in men with varying profiles of strength and aerobic power

Hemodynamic, cardiac, and hormonal responses to lower-body negative pressure (LBNP) were examined in 24 healthy men to test the hypothesis that responsiveness of reflex control of blood pressure during orthostatic challenge is associated with interactions between strength and aerobic power. Subjects underwent treadmill tests to determine peak oxygen uptake ( O_2max) and isokinetic dynamometer tests to determine knee extensor strength. Based on predetermined criteria, subjects were classified into one of four fitness profiles of six subjects each, matched for age, height, and body mass: (a) low strength/average aerobic fitness, (b) low strength/high aerobic fitness, (c) high strength/average aerobic fitness, and (d) high strength/high aerobic fitness. Following 90 min of 0.11 rad (6°) head-down tilt (HDT), each subject underwent graded LBNP to –6.7 kPa or presyncope, with maximal duration 15 min, while hemodynamic, cardiac, and hormonal responses were measured. All groups exhibited typical hemodynamic, hormonal, and fluid shift responses during LBNP, with no intergroup differences between high and low strength characteristics. Subjects with high aerobic power exhibited greater (P < 0.05) stroke volume and lower (P < 0.05) heart rate, vascular peripheral resistance, and mean arterial pressure during rest, HDT, and LBNP. Seven subjects, distributed among the four fitness profiles, became presyncopal. These subjects showed greatest reduction in mean arterial pressure during LBNP, had greater elevations in vasopressin, and lesser increases in heart rate and peripheral resistance. Neither O_2max nor leg strength were associated with fall in arterial pressure or with syncopal episodes. We conclude that interactions between aerobic and strength fitness characteristics do not influence responses to LBNP challenge.     

Magnitude and decay of stretch-induced enhancement of power output

There is ample evidence that the pre-stretching of a muscle enhances performance of the subsequent shortening or concentric contraction. The purpose of this study was to investigate this stretch-induced enhancement in terms of the effect of load on the magnitude and decay of the muscle's power output. Instantaneous, mean and peak power outputs were compared between concentric-only and rebound bench press throws at different loads. The maximal strength [1 RM=84.0 (10.5) kg] of 18 male subjects [21.1 (3.0) years, 87.2 (11.9) kg] was determined using an isoinertial Smith press machine. The results of this study indicate enhancement of concentric motion by prior eccentric muscle action (200–780% enhancement in the first 100 ms). However, the magnitude and temporal characteristics of this enhancement differed across loads. Using a lighter load produced greater initial enhancement (P<0.05) but the decay of this enhancement was more rapid. The heavier 80% 1 RM loading showed a later time to peak enhancement (80 ms versus 20 ms) and slower decay of the stretch induced augmentation (460 ms versus 260 ms). It is concluded that the degree of stretch–shorten cycle enhancement differs according to the load and the time-dependent characteristics of the motion. Electronic Publication     

Adolescent motor skill and performance: Is physical activity in adolescence related to adult physical fitness?

In the Amsterdam Growth and Health Longitudinal Study (AGAHLS), a cohort of about 400 boys and girls (mean age 13 years) were followed over a period of 20 years. Over that period repeated measurements were done of body dimensions (height, weight, skinfolds), physical fitness (eight motor performance field tests: plate tapping, bent arm hang, 10 × 5 m sprint, arm pull, sit and reach, standing high jump, 10 leg lifts, 12‐min endurance run, and one laboratory test to measure maximal aerobic power), and physical activity (by a cross‐check interview). Three research questions were studied: (1) Is there a positive relationship between adolescent fitness (age 13–17 years) and adult physical activity (age 33 years)? (2) Do physical fitness and physical activity track from adolescence into adulthood? (3) What is the longitudinal relationship between physical fitness and physical activity? Multiple linear regression analysis showed that of the 9 physical fitness tests, only the 12‐min endurance run and the maximal aerobic power during adolescence are significant (P < 0.05) predictors of adult physical activity. The effects are not influenced by biological age but by sex: only in females are the predictions significant (P < 0.05) Tracking over the period of 20 years estimated from stability coefficients showed values for physical fitness varying between 0.83 (plate tapping) to 0.38 (standing high jump and maximal aerobic power). Physical activity shows lower stability coefficients (0.35–0.29). A longitudinal linear regression technique was used to analyse the relationship between physical activity and physical fitness over the 20‐year period; in this analysis corrections were made for both time‐dependent (time, biological age, and cardiovascular factors) and time‐independent variables (sex). All physical fitness tests show positive and significant (P < 0.05) standardized regression coefficients with physical activity, but the explained variance is less than 1%. Only maximal aerobic power has a higher explained variance of 1.8%. It can be concluded that: (1) Physical fitness in adolescence is only weakly related to adult physical activity; (2) between age 13 and 33 years, physical activity has low stability and physical fitness was higher stability; and (3) the longitudinal relationships between physical fitness and physical activity are only meaningful with maximal aerobic power. Am. J. Hum. Biol. 13:180–189, 2001. © 2001 Wiley‐Liss, Inc.     

Effect of nutritional supplementations on physical performance and muscle strength parameters in older people: A systematic review and meta-analysis

Malnutrition plays a role in the development of poor physical performance, frailty and sarcopenia. The use of nutritional supplementations for improving physical performance and muscle strength parameters in older people is unclear. We therefore aimed to summarize the effect of nutritional supplementations compared to placebo on physical performance (i.e. tests more investigating physical function, utilising aerobic capacity & muscle power) and muscle strength (i.e. tests depending on muscle power) outcomes in older people in randomized controlled trials (RCTs). A literature search in major databases was undertaken until the 01st September 2018. Eligible studies were RCTs investigating the effect of nutritional supplementations vs. placebo in older people (people having an age >60 years). Standardized mean differences (SMD) and 95% confidence intervals (CIs) were used through a random effect model. Over 4007 potentially eligible articles, 32 RCTs for a total of 4137 older participants (2097 treated and 2040 placebo) (mean age: 76.3 years; 65% females) were included. Compared to placebo, multi-nutrient supplementations significantly improved chair rise time (n = 3; SMD=-0.90; 95%CI: -1.46 to -0.33; I² = 87%). Multi-nutrients significantly improved handgrip strength when compared to placebo (n = 6; 780 participants; SMD = 0.41; 95%CI: 0.06 to 0.76; I² = 79%), as did nutritional supplementations including protein (n = 7; 535 participants; SMD = 0.24; 95%CI: 0.07 to 0.41; I² = 16%).Nutritional supplementations also led to a significant improvement in chair rise time and in handgrip strength in participants affected by frailty/sarcopenia and in those affected by medical conditions. In conclusion, nutritional supplementation can improve a number of physical performance outcomes in older people, particularly when they include multi-nutrients and in people already affected by specific medical conditions, or by frailty/sarcopenia.     

Development,validity and reliability of a new pressure air biofeedback device (PAB) for measuring isometric extension strength of the lumbar spine

This study describes the development of a new portable muscle testing device, using air pressure as a biofeedback and strength testing tool. For this purpose, a pressure air biofeedback device (PAB^®) was developed to measure and record the isometric extension strength of the lumbar multifidus muscle in asymptomatic and low back pain (LBP) persons. A total of 42 subjects (age 47.58 years, ±18.58) participated in this study. The validity of PAB^® was assessed by comparing a selected measure, air pressure force in millibar (mb), to a standard criterion; calibrated weights in kilograms (kg) during day-to-day tests. Furthermore, clinical trial-to-trial and day-to-day tests of maximum voluntary isometric contraction (MVIC) of L5 lumbar multifidus were done to compare air pressure force (mb) to electromyography (EMG) in microvolt (μV) and to measure the reliability of PAB^®. A highly significant relationship were found between air pressure output (mb) and calibrated weights (kg). In addition, Pearson correlation calculations showed a significant relationship between PAB^® force (mb) and EMG activity (μV) for all subjects (n?=?42) examined, as well as for the asymptomatic group (n?=?24). No relationship was detected for the LBP group (n?=?18). In terms of lumbar extension strength, we found that asymptomatic subjects were significantly stronger than LBP subjects. The results of the PAB^® test differentiated between LBP and asymptomatic subject’s lumbar isometric extension strength without any risk to the subjects and also indicate that the lumbar isometric extension test with the new PAB^® device is reliable and valid.     

A 15-year physical activity pattern is positively related to aerobic fitness in young males and females (13–27 years)

The purpose of this paper is to test the hypothesis that daily physical activity over a period of 15 years has been beneficial to aerobic fitness in young male and female participants (13–27 years) in the Amsterdam Growth and Health Longitudinal Study. Only subjects with the maximal data of six sets of measurements were included (83 male and 98 female participants). Daily physical activity was assessed using a standardized interview on activity and expressed as a weighted activity score. Aerobic fitness was assessed using a maximal running test on a treadmill and measuring the maximal oxygen uptake ( ) and the maximal slope of the track (S _max). To assess the longitudinal relationship between daily physical activity and aerobic fitness a real longitudinal analysis was carried out with generalized estimating equations, adjusting for differences in initial aerobic fitness at age 13, and for other lifestyle (dietary intake, smoking and alcohol consumption) and biological parameters (biological age, body fat, blood pressure and concentration of serum cholesterol). A significant relationship (P<0.01) was observed between daily physical activity and both and S _max. It can be concluded that the development of aerobic fitness between the age of 13 and 27 years is independently and positively related to daily physical activity in this group of male and female participants in the study. The functional implications, however, are small: a relatively high increase in the weighted physical activity score of 30% over a period of 15 years results in a 2%–5% increase in aerobic fitness. Electronic Publication     

基于肌电信号时频分析的腰背部肌肉功能评价方法研究

肌电信号在评价下腰痛病人背部肌肉功能的研究中得到广泛应用，但是由于肌电信号本身的个体差异很大，往往掩盖被测对象真正的生理差异。本文对采集自腰背部的8通道肌电信号进行研究，对时一频域计算瞬时中频的算法做了改进。并根据正常组和病人组肌电信号的时频谱能量聚集程度不同这一发现提出了一种以能量离散度为指标的区分方法。     

Abdominal muscle size and symmetry at rest and during abdominal hollowing exercises in healthy control subjects

The symmetry of, and physical characteristics influencing, the thickness of the lateral abdominal muscles at rest and during abdominal exercises were examined in 57 healthy subjects (20 men, 37 women; aged 22–62 years). M-mode ultrasound images were recorded from the abdominal muscles at rest and during abdominal hollowing exercises in hook-lying. The fascial lines bordering the transvs. abdominis, obliquus internus and obliquus externus were digitized and the absolute thickness, relative thickness (% of total lateral thickness) and contraction ratio (thickness during hollowing/thickness at rest), as well as the asymmetry (difference between sides expressed as a percent of the smallest value for the two sides) for each of these parameters were determined for each muscle. Both at rest and during hollowing, obliquus internus was the thickest and transvs. abdominis the thinnest muscle. There were no significant differences between left and right sides for group mean thicknesses of any muscle; however, individual asymmetries were evident, with mean values for the different muscles ranging from 11% to 26%; asymmetry was much less for the contraction ratios (mean % side differences, 5–14% depending on muscle). Body mass was the most significant positive predictor of absolute muscle thickness, for all muscles at rest and during hollowing, accounting for 30–44% variance. Body mass index explained 20–30% variance in transvs. abdominis contraction ratio (negative relationship). The influence of these confounders must be considered in comparative studies of healthy controls and back pain patients, unless groups are very carefully matched. Asymmetries observed in patients should be interpreted with caution, as they are also common in healthy subjects.     

Lumbar paraspinal muscle fatigability in repetitive isoinertial loading: EMG spectral indices, Borg scale and endurance time

The purpose of this study was to develop a submaximal repetitive isoinertial back muscle endurance test by defining the relationships between the power spectral indices of paraspinal muscle electromyographic (EMG) activities, endurance time and a subjective estimate of fatigue (Borg scale). Bilateral surface EMG recordings were obtained over the lumbar paraspinal muscles in ten individuals who were currently free from back pain. All subjects performed repetitive upper trunk extensions (25° flexion and 5° extension, 30 repetitions per min), while movement below the third lumbar vertebral body was mechanically restricted. The load level depended upon upper body mass, sex, and age. The tests continued for as long as the subjects were able to maintain the required repetition rate (endurance time). Median (MF) and mean power frequency (MPF) slopes were calculated by performing a fast Fourier transformation after confirmation of EMG stationarity by recurrence quantification analysis. MF and MPF correlations with endurance time/Borg scale were measured for the first 60 s (0.60–0.88/0.42–0.86), the first 90 s (0.62–0.89/0.52–0.90), the first 120 s (0.50–0.76/0.41–0.73), and the entire repetitive run (0.63–0.88/0.54–0.90). To test for the reproducibility of the spectral indices, EMGs were recorded for 2 min during repetitive loading from the same subjects on two consecutive days. Corresponding spectral slopes of MF and MPF were correlated at 60 s (0.36–0.93), 90 s (0.58–0.92), and 120 s (0.70–0.94) at the L3–L4 and L5–S1 levels, indicating good reproducibility of results from alternate recording sessions at the L5–S1 level. It is concluded that paraspinal muscle spectral indices (MF and MPF) measured before the onset of total muscle fatigue are good predictors of endurance time and are closely related to the subjective perception of fatigue.     

Effect of one- and two-leg training on arm and two-leg maximum aerobic power

Summary The purpose of this study was to examine the effect of one- and two-leg training on arm and two-leg maximum aerobic power. Seven subjects cycle-trained both legs simultaneously for 30 min·day^–1, 4 days·week^–1 for 4 weeks. Nine subjects cycle-trained each leg 15 min·day^–1, 4 days· week^–1 for 4 weeks. Both groups trained at a heart rate equal to that measured at 75% of their two-leg maximum aerobic power. Thus, during each training session the groups performed 30 min of work at the same heart rate intensity. Five subjects served as a non-training control group. Arm and leg maximum oxygen uptake tests were conducted before and after training. Only two-leg training induced significant gains in arm aerobic power (P<0.0003), whereas both modes of training resulted in signifcant increases in two-leg aerobic power (P<0.0008). The data demonstrate that improvements in arm aerobic power were dependent on the quantity of leg muscle mass involved in the training, whereas gains in two-leg aerobic power occurred regardless of whether the legs were trained separately or simultaneously.